Thiols protect the inhibition of myocardial aconitase by peroxynitrite.
Peroxynitrite (ONOO-) is a potent inhibitor of myocardial aconitase. Because ONOO- reacts with sulfhydryl moieties, we investigated whether thiols protect against ONOO(-)-mediated inhibition of aconitase. Aconitase activity was examined in ventricular homogenates prepared from freshly isolated rat hearts. Peroxynitrite, but not the nitric oxide donor S-nitroso-N-acetyl-d,l-penicillamine (0.03-300 microM), inhibited aconitase activity (IC50 = 47 +/- 6 microM). L-Cysteine (0.03-3 mM), glutathione (0.03-3 mM), and N-(2-mercaptoproprionyl)-glycine (MPG, 0.1-3 mM) protected against the inhibitory effect of ONOO- (100 microM) with the rank order of potency of MPG > glutathione > L-cysteine. D-Cysteine (3 mM) had a protective effect similar to L-cysteine, but L-cystine, the oxidized form of L-cysteine, offered no protection. Ferrous ammonium sulfate (1 mM) markedly enhanced the protection provided by L-cysteine, but not by glutathione or MPG. Thiols protect myocardial aconitase against inhibition by ONOO- in a manner which is sulfhydryl group dependent and not stereospecific. The protection is related to the maintenance of the redox state of the iron-sulfur cubane cluster and cysteine residues at the active site of the enzyme. Both naturally occurring thiols and thiol-based drugs may be useful to protect the heart during ischemia-reperfusion injury where there is an excessive production of ONOO-.
Cheung
P Y
PY
Department of Pediatrics, University of Alberta, Edmonton, Canada.
Danial
H
H
Jong
J
J
Schulz
R
R
D000154:Aconitate Hydratase / Q000037:antagonists & inhibitors*; D000818:Animals; D002951:Citrates / Q000494:pharmacology; D003545:Cysteine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005296:Ferrous Compounds / Q000494:pharmacology; D005978:Glutathione / Q000494:pharmacology; D005998:Glycine / Q000494:pharmacology / Q000031:analogs & derivatives; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D009566:Nitrates / Q000494:pharmacology*; D010396:Penicillamine / Q000031:analogs & derivatives / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D026423:S-Nitroso-N-Acetylpenicillamine; D013438:Sulfhydryl Compounds / Q000494:pharmacology*
D002951:Citrates; D005296:Ferrous Compounds; C110658:N-(2-mercaptoproprionyl)-glycine; D009566:Nitrates; D000644:Quaternary Ammonium Compounds; D013438:Sulfhydryl Compounds; C039642:peroxynitric acid; C007744:fluorocitrate; D026423:S-Nitroso-N-Acetylpenicillamine; C038178:ammonium ferrous sulfate; D000154:Aconitate Hydratase; D005978:Glutathione; D010396:Penicillamine; D003545:Cysteine; D005998:Glycine